In recent years, particularly in emergency medicine, it has come to be known to significantly improve a rehabilitation rate of a cardiac arrest patient by emergency life-saving measures by a doctor or an emergency medical technician while a regional saturation of oxygen (rSO2) of the cardiac arrest patient is monitored using a near-infrared ray (for example, refer to Patent Literatures 1 and 2). Generally, for example, as illustrated in FIG. 1 of Patent Literature 2, a structure of an apparatus for monitoring a regional saturation of oxygen (rSO2) using a near-infrared ray is separated into a probe unit attached to the forehead of a patient's head and an apparatus main body unit having a circuit board for analyzing a signal from the probe unit and a display unit for displaying an analysis result integrated, and the probe unit and the apparatus main body unit are connected with a long signal cable.